RESEARCH INVOLVEMENT
To complement its current undergraduate research participant crew, the
Dieckmann group is looking for several (preferentially MS&E) sophomores to
participate in two different research projects beginning in Fall 2010. One of
the projects deals with defects and transport in transition metal
orthosilicates and the second one with the study of mixed glass former
phenomena in certain glasses. Detailed project descriptions are given below.
If you should be
interested in participating in one of the projects denoted above, please
contact
Rüdiger Dieckmann
228 Bard
Hall
phone:
607-255-4315
E-mail: dieck@ccmr.cornell.edu
This is an ongoing NSF-supported research program.
The project deals with point defects and the orientation-dependent transport of
matter and charge in orthosilicates, i.e., ternary oxides of the type Me2SiO4.
In the orthosilicates of interest Me is a transition metal, i.e., Co or Mn.
Some investigations on defects and transport of matter and charge in
orthosilicates with Me = Fe have been performed in the Dieckmann lab some time
ago. The results from this earlier work have revealed a very significant
anisotropy in the diffusion of iron and in the electrical conduction. The more
recent research is to find out whether this anisotropy is a common feature of
orthosilicates with Me being transition metals or not and how the anisotropies
change with the type of Me. The work performed includes the growth of
orthosilicate single crystals with different orientation and different
composition, i.e., with Me = Co or Mn, measurements of the variation of the
oxygen content of Me2SiO4+δ with the oxygen partial
pressure at different temperatures and measurements of tracer diffusion
coefficients for Me (= Co or Mn, respectively) for different crystal
orientations. At present, the focus is on an orthosilicate with Me = Mn which
is called tephroite.
Currently, several undergraduate students are
participating in this program. They are involved in the preparation of
manganese orthosilicate samples (powder synthesis via both a traditional
ceramic route and a sol-gel synthesis route, making polycrystalline feed rods
for single crystal growth, single crystal growth by the floating zone
technique, cutting and grinding of single crystal samples, etc.), and the
characterization of samples (density, microstructure, phase purity, crystal
orientation, dislocation density, etc.).
Measurements of cation tracer diffusion coefficients as a function of
temperature and oxygen activity in cobalt orthosilicate samples have been
performed. Measurements of cation tracer diffusion coefficients are planned to begin
soon for manganese orthosilicate samples. Undergraduate students are expected
to perform a very significant fraction of these experiments and also to
participate in sample preparation and characterization.
The NSF-supported project “Study of Mixed Glass
Former Phenomena in Materials” is part of an international collaborative
educational and research program within the NSF-DMR sponsored Materials World
Network. Collaborators in the U.S. are from Iowa State University (Steve W.
Martin) and from Central Michigan University (Valeri Petkov). Collaborators in
The project at Cornell
deals with the tracer diffusion of cations in the type of glasses denoted
above. The glasses investigated at Cornell were prepared by Corning Inc. The Dieckmann
group has measured sodium tracer diffusion coefficients as a function of
temperature, glass composition in glasses of the type (Na2O)0.2·[(BO1.5)x(SiO2)1-x]0.8
using the radioactive isotope Na-22. The observed temperature and composition
dependencies are intended to be linked to structural observations made by
collaborating groups. Glasses of other compositions to be investigated in the
future are currently under discussion.
Since water incorporated into oxide glasses can significantly
influence many glass properties, the Dieckmann group also investigates the
uptake of water by oxide glasses and the influence of water taken up by such
glasses during diffusion-annealing or during pre-annealing on the tracer
diffusion of cations. The analytical being used for detecting OH-groups
generated due to an uptake of water by oxide glasses is an FT-IR spectrometer
with a microscope attached to it.
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